In the prior art, there are many methods of coating various silicone-based resins to improve the separating, water-repelling, electrically insulating, water-resistant, heat-resistant, humidity-resistant, weather-resistant, solvent-resistant and other properties concerning the durability of various substrates. However, the silicone resins have low transparency. Therefore, if they are to be coated while retaining the color tone or luster of the substrate, coating should be very thin. However, the silicone resins have low hardness and hence inferior scratch-resistant property. This means that reducing the coating film thickness leads to deterioration of the durability. Accordingly, it has been proposed to increase the hardness of the coating film by making use of crosslinking reactions obtained by introducing epoxy groups or vinyl groups into the molecules of the silicone resins or increase the hardness of the coating film by incorporating such fillers as fine particles of silica, alumina, antimony, etc.
In another aspect, in an extensively employed well-known method of manufacturing fluorocarbon-based coating films, the surface of a metal substrate such as aluminum, steel or stainless steel is roughened by means of wire brushes or chemical etching, then a primer is coated. A paint prepared by suspending fine particles of a fluorocarbon-based material such as ethylene polytetrafluoride in ethanol or the like, is coated. Then, the substrate is dried and baked at a temperature of about 400.degree. C. for about one hour, thus fixing a fluorocarbon-based polymer on the substrate surface.
With this method, the polymer coating can be readily obtained. However, since the polymer is bonded to the substrate merely by an anchor effect, its adhesion to the substrate is limited. In addition, the coating film surface is flattened because of the baking at a high temperature of 400.degree. C. Therefore, a satisfactory water- and oil-repelling surface can not be obtained. Therefore, this method is insufficient for devices which desirable have water- and oil-repelling coating films, such as electric products, vehicles and industrial devices.
Further, there are methods of plasma treatment for rendering the surface of fluorocarbon-based coating films hydrophilic. However, none of them permits satisfactory characteristics to be obtained.